What is CVE-2026-64531?
In the Linux kernel, the following vulnerability has been resolved: net: openvswitch: reject oversized nested action attrs Open vSwitch stores generated flow actions as nlattrs, whose nla_len field is u16. Commit a1e64addf3ff ("net: openvswitch: remove misbehaving actions length check") allowed the total sw_flow_actions stream to grow beyond 64 KiB, which is valid, but also removed the last guard preventing a generated nested action attribute from exceeding U16_MAX. An oversized generated container can thus be closed with a truncated nla_len. A later dump or teardown then walks a structurally different stream than the one that was validated. In particular, an oversized nested CLONE/CT action may cause subsequent bytes in the generated stream to be interpreted as independent actions. Keep the larger total-action-stream behavior, but make nested action close reject generated containers that do not fit in nla_len, and return the error through all callers. For recursive SAMPLE, CLONE, DEC_TTL, and CHECK_PKT_LEN builders, trim resource-owning action-list tails in reverse construction order before discarding failed wrappers, so resources copied into the rejected tails are released before the wrappers are removed. Most failed outer wrappers are discarded by truncating actions_len after child resources have been released. CHECK_PKT_LEN also trims its parent after branch resources are gone. SET/TUNNEL close failures unwind their known tun_dst ownership directly, and SET_TO_MASKED has no external ownership and truncates on close failure.
Timeline
- 2026-07-27Published to the U.S. National Vulnerability Database (NVD)
- 2026-08-01NVD record last updated
Affected product
See advisory
Remediation Steps
- Identify systems running Linux kernel with Open vSwitch enabled
- Apply available kernel security patches for the OVSwrap vulnerability
- Verify patch installation and reboot systems as required
- Monitor for indicators of exploitation (local privilege escalation attempts)
- Restrict local access on affected systems to minimize attack surface
References
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 1 of August 2026 (August 3 – 9)
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